p ~ AI. A B A M A~ COO P El\A T IV !l

Extens1on SYSTEM

CIRCULAR ANR-973

Anaerobic Lagoons Anaerobic lagoons are earth­

en structures, which look at first glance like farm ponds. These lagoons are designed to provide biological treatment and long­term storage of animal waste. Anaerobic lagoons are larger than manure storage basins, which do not provide significant biological treatment or long stor­age periods, but smaller than aerobic lagoons. Even though aerobic lagoons are designed to provide a higher degree of treat­ment with less odor, anaerobic lagoons decompose more organ­ic matter per unit volume. Because of their treatment and storage capabilities anaerobic la­goons are a good compromise between storage basins and aer­obic lagoons.

Anaerobic treatment of waste occurs without free oxygen to liquify or degrade high BOD (biochemical oJ..rygen demand) organic waste. With proper de­sign and management the anaer­obic lagoon can function for years. Odor from a well­designed and well-managed la­goon will be only slightly musty; foul odor indicates a malfunction requiring corrective action.

Advantages of anaerobic la­goon systems are:

• Manure can be handled with water flushing systems, sewer lines, pumps, and irriga­tion equipment.

• The high degree of stabi­lization reduces odors during land application.

ALABAMA A&M AND AUBURN UNIVERSITIES

Planning And Managing Lagoons For

Swine Waste Treatment

• High nitrogen reduction minimizes the land area required for liquid effluent disposal.

• Long-term storage is pro­vided at low cost.

Disadvantages of anaerobic lagoons include:

• Public perception that a la­goon is an open container of manure.

• Offensive odors if improp­erly designed and maintained.

• Limited nitrogen availability if manure is used as a fertilizer.

Location Requirements Ideally, lagoons should be

located downslope from the swine housing unit so that waste can be drained or flushed to the lagoon by gravity. Because recy­cled lagoon water is generally used to flush waste from build­ings, location should be close enough for easy access for the recycle system.

American Society of Agricultural Engineering (ASAE) Engineering Practice 403.3 rec­ommends that lagoons be no less than 300 feet from any water wells to prevent water supply contamination. Natural Resources Conservation Service (NRCS) recommends 500 feet but will accept 150 feet from an upslope well.

Location of lagoons with re­spect to nonoperator-owned res­idences is an important consider­ation. ASAE recommends a minimum of 900 feet downwind. In Alabama, however, recom-

mendations are that lagoons be (1) located at least Y4 mile from property lines and nonoperator­owned residences and (2) screened from view with a nat­ural or constructed screen. In some situations, especially in north Alabama, the location of a lagoon will be controlled by soil and geological considerations.

Soils Investigation Although printed county soil

survey maps give general guid­ance, the swine operator plan­ning a treatment lagoon should have an on-site subsurface soils investigation made. Agencies with expertise similar to the NRCS can conduct on-site soils investigations and make appro­priate recommendations. Soil borings or backhoe excavations are standard procedures to iden­tify shallow soil over coarse sand and gravel, crevices, limestone, or permeable bedrock. If any of these conditions exist, proce­dures and materials, such as clay liners, geotextile liners, or con­crete, to prevent seepage to ground water must be used in construction.

NRCS currently offers this on-site soils and geologic investi­gation assistance for animal waste management structures as part of the animal waste man­agement technical assistance program. They should be con­tacted for assistance. This process will determine the soil suitability for and final location of a swine waste lagoon.

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Lagoon Design­Volume

Proper design of an anaero­bic lagoon system requires t~e calculation of volume that w1ll be needed to accommodate waste accumulation over the de­sired treatment period. Total la­goon volume of either a si?gle stage or two-stage system 1s composed of several parts:

• Treatment volume. • Manure wastewater vol­

ume. • Surface runoff volume. • Net rainfall (rainfall minus

surface evaporation, including the 25-year-24-hour storm).

• Sludge volume. • Freeboard volume. Treatment volume provides

enough dilution volume for the breakdown of volatile solids by bacteria and is not removed from the lagoon during pump­down operations. This volume is based on volatile solids daily loading rate in pounds per day per thousand cubic feet. Typica~ recommended primary anaerob1c lagoon minimum treatment vo.l­ume for swine waste lagoons m Alabama ranges from 6 to 6.5 pounds of volatile solids per thousand cubic feet per day. This is around 1 cubic foot per pound of average live weight for farrow-to-weanling and farrow­to-feeder operations and up to 1.5 cubic feet of permanent vol­ume per pound of average live weight for weanling-to-feeder, feeder-to-finish, and farrow-to­finish operations.

Manure wastewater vol­ume provides for wastewater storage equal to the accumulated manure volume over the de­signed treatment period. Pump­down interval and manure treat­ment period are the same and should be 180 days in Alabama. Storage volume per pound of av­erage live weight is 0. 5 cubic

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foot for 6 months. Longer treat­ment time offers greater flexibili­ty in scheduling pumping opera­tions.

Surface runoff volume provides storage for rainfall runoff plus any wash water or other freshwater that may be used for cleaning buildings or lot areas. This volume is removed from the lagoon during pumping operations. Manure-free runoff from open areas, unless needed for filling or dilution, should be diverted away from the lagoon. Generally the amount of rainfall and runoff to be collected and stored in the lagoon is figured on the wettest 10 years for net rainfall less evaporation on la­goon surface and berm runoff.

Netrainfall.Thelagoon must provide storage for the net gain of rainfall minus lagoon surface evaporation plus the berm area runoff plus the 25-year-24-hour storm. In Alabama, typical annual rainfall is at least 12 inches more than evaporates from a free water surface. Surface area and berm runoff can add as much as 4 feet per year. This volume from rainfall less evaporation is held in the second stage of a two-stage la­goon and removed when the la­goon is pumped.

Sludge volume results from manure solids entering a swine lagoon and a portion remaining in the first stage as bottom sludge. Recent research on feed­er-finish units in North Carolina indicates that approximately 0.034 cubic feet of sludge accu­mulates per year per pound of average swine live weight. Solids separation with a properly oper­ating settling tank can cut sludge accumulation in half. The sludge accumulation rate can be used to determine volume necessary for sludge over any particular cho­sen design time, up to 12 to 15 years by some designers. Recommended sludge volume is

0.5 cubic foot per pound of av­erage swine live weight.

Freeboard volume is the minimum extra depth above total full pool level, usually 1 foot after all other volume re­quir~ments are met. Figures 1 and 2 show a cross section of one- and two-stage lagoon de­signs, which may be used throughout Alabama. Surface area will vary with depth.

Two-Stage Lagoons Where space is available, a

two-stage lagoon should be con­structed to improve wastewater treatment and management flexi­bility. For swine operations where lagoon liquid is recycled for open gutter flushing and ani­mals have direct access to flush water a second stage lagoon provides some insurance against disease organisms being re­turned from the first stage la­goon before a reasonable die-off period. In addition to further treatment, the second stage la­goon also stores treated waste­water for irrigation to further treatment. This treated waste­water can be irrigated through small diameter sprinkler nozzles.

A second stage lagoon should allow for a permanent volume that cannot be pumped (2-foot minimum), wastewater volume for the desired treatment period (180 days minimum), sur­face runoff volume for the de­sired treatment period, net rain on both stages, and space for the 25-year-24 hour storm for both stages (see Figure 2). The first stage will contain only the treatment (permanent) volume and sludge volume.

Lagoon Design­Geometry

Swine waste lagoons can be designed in a variety of shapes. However, circular or square la-

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start pumping

r-24-hour storm

surface runoff volume

manure wastewater volume

treatment volume

Figure i . Capacity of single-stage anaerobic lagoon.

manure wastewater volume 2-ft. minimum

volume for recycle

net rainfall

stop pumping

FIRST STAGE Treatment

SECOND STAGE Storage And Treatment

Figure 2. Capacity of two-stage anaerobic lagoon.

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goons allow easier mixing with propeller or pump type agitators and are usually less expensive to construct. When rectangular la­goons are constructed, a 4:1 length to width ratio should not be exceeded to encourage even distribution of manure.

Typical lagoon depths range from 8 to 20 feet, with a mini­mum depth of 8 feet. The specif­ic footage depends on animal numbers, runoff area slope, and underground geology. Deeper lagoons offer several advantages, including less land needed be­cause of smaller surface area re­quirement, more thorough mix­ing of lagoon contents by rising gas bubbles, efficient mechanical aeration, and minimum odor.

The dike for a lagoon must be a minimum of 8 feet wide. Slopes on earthen dikes and banks generally range between 2:1 and 3:1. To establish good grass covers and for safe mow­ing, slopes of 3:1 or better are recommended. Generally, slopes below the waterline are 2:1 though this depends on soil type and structure design.

An emergency spillway must be provided in the s&ond stage of a two-stage system to protect the dam from extreme flooding. The spillway should be placed a minimum of 1 foot below the top of the berm with allowance for settling. It should be located as close to natural ground as possible and as far as possible from a corner location. The spill­way is intended for use in flood conditions and is not to be used as a drain instead of pumping down the lagoon.

Construction Techniques

Proper lagoon construction is essential to ensure protection of ground water resources as well as to provide a system that will operate effectively for many

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years. Most guidelines for ac­cepted lagoon construction tech­niques include:

• Site preparation. • Excavation. • Embankments • Cutoff trench. • Sealing. Site preparation requires

that all trees, grass, and organic material be removed. Topsoil should be stockpiled close to the construction site for later place­ment on the top and exposed sides to allow good establish­ment of grass. After stripping, the foundation area should be prepared to bond with the fill. Loose dry material should be re­moved and the foundation area scarified, disked, adjusted for moisture, and compacted as nec­essary.

Excavation requires the re­moval of rocks, sand pockets, gravel, and other materials not suitable for sealing. The excava­tion should be deep enough for both proper volume and seal construction.

Lagoon embanktnents should be constructed to allow for usual settling of 5 percent. The embankment should be planted with a cover grass to prevent erosion and must be large enough to accommodate mowers. Suitable fill materials should be free of sand, roots, stones more than 6 inches in di­ameter, and other objectionable material. The minimum moisture content of the fill material and foundation should allow the for­mation of a ball that will not separate when squeezed by hand. Experience has shown that with suitable soil material (with enough clay content) three passes of a sheepsfoot roller per 6-inch fill lift on the embank­ment or bottom seal will provide adequate compaction for sealing.

A cutoff trench may be re­quired to remove sand, gravel,

or other water-conducting mate­rials to prevent leakage under the embankment.

Sealing is required on the bottom and sides of the lagoon to protect ground water. Seal construction guidelines generally call for overexcavation and then backfilling and recompaction of seal materials in thicknesses not exceeding 6 inches compacted depth (not more than 9 inches deep for compaction).

The lower 6 inches of the bottom seal may be scarified and compacted in place to eliminate removal and replacement. In general, a minimum of 1-foot thick clay seal must be provided on the bottom and sides of a la­goon. The deeper the lagoon, the thicker the required seal, up to or beyond 4 feet for a water depth of 25 feet.

Some soils require soil amendments such as bentonite, soda ash, or artificial liners to obtain a proper seal. Most prop­erly planned swine waste la­goons receiving raw manure eventually seal, limiting soil per­meability to as little as 10-6 em/ sec. Immediately after con­struction, the lagoon seal should be covered with water (at least 2 feet deep above the highest bot­tom elevation) to prevent drying and cracking.

Solids Exclusion And Agitation

Some manure solids break down very slowly or not at all in a lagoon. This nondegradable material leads to sludge buildup, which interferes with the pump­out procedure. As much of these solids as possible should be sep­arated from the manure waste stream and kept from entering the lagoon. Over time the accu­mulated solids will reduce waste treatment volume and cause "overloading" of the lagoon. This "overloading" causes increased

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odor and reduced waste treat­ment function.

As solids accumulate into the waste treatment volume, they should be removed to prevent overloading by a special pump­out procedure called lagoon renovation. This requires con­tinuous agitation with specially designed propeller or chopper pump agitators during the pump-out procedure. For further information on this see Extension Circular ANR-953, "Renovating Livestock Lagoons Using Irrigation."

Management Procedure Proper management is essen­

tial to ensure that a lagoon func­tions effectively and efficiently during its expected lifetime. Good design and well-executed construction are worthless if the lagoon is not properly managed.

For a lagoon system to oper­ate successfully, start-up proce­dures must be followed careful­ly. A new lagoon should be filled with water to 60 percent of treatment volume before manure is introduced. This assures suffi­cient dilution for the establish­ment of bacterial activity and will also minimize start-up odors. Starting a lagoon in late spring or early summer will

allow a good bacterial popula­tion to be established during the warm season.

After initial start-up, lagoons perform best when they are loaded continuously. Flushing systems provide ideal loading conditions for lagoons.

If foul odors develop in an anaerobic lagoon, the pH level should be checked. A pH read­ing can be made using soil test­ing equipment or litmus paper. The addition of hydrated lime will increase a pH that is too low (less than 6.5). A higher pH will increase the activity of methane bacteria and decrease the acid concentration. If this treatment does not greatly reduce and con­trol foul odors, the lagoon is probably overloaded.

Lagoons usually fill to design capacity within 2 to 3 years of start-up with the accumulation of wastes and rainfall on the open lagoon surface. To prevent la­goon overflow, excess lagoon liquid should be applied to grassland, cropland, or wood­land at rates within the soil infil­tration capacity and the fertilizer requirement of the vegetation. Lagoons should be pumped dur­ing the growing season to allow enough storage space for waste­water accumulation through

winter when crop growth and nutrient requirements are low.

The lagoon liquid should be sampled and analyzed to deter­mine its nutrient content. Table 1 gives information on average feeder-to-finish lagoon liquid ac­cumulation rates and estimated available nutrient contents. Table 2 estimates application rates and minimum land areas needed for feeder-to-finish lagoon liquid ir­rigation application for different crops.

Wastewater irrigation using regular irrigation equipment is the easiest and most cost -effec­tive way to apply lagoon liquid to land. Lagoon liquid should be irrigated on days with low hu­midity and when winds are not blowing toward neighboring res­idences. Irrigating in the early morning and early in the week will reduce offensive odors.

For more information on land applying swine waste from lagoons refer to Extension Circular ANR-925, "Calibrating Traveling Guns For Slurry Irrigation." Procedures described apply to wastewater irrigation from lagoons.

As lagoons age, salt concen­trations may increase to levels that can inhibit bacterial activity. Salt buildup in lagoons should

Table 1. Fertilizer Nutrients In Swine Feeder-To-Finish Lagoon Liquid.

Total Anaerobic Total Lagoon Plant Available Nutrientsb

Lagoon Liquid Liquid To Be Total

Irrigated a/ Nutrients Capacity, Animal/ Plant Irrigated Soil Incorporated

Ft3/Animal Year Nutrient

One Two-stage Acre- Lbs./ Lbs./ Lbs./

Lbs./ Lbs./

Stage 1st+ 2nd Gallons Inch Acre-Inch Acre-Inch Animal/

Acre-Inch Animal/ Year Year

270 200 + 70 927 0.034 N 136 68 2.3 96 3.3 Pz05 53 37 1.3 40 1.4 K20 133 93 3.2 100 3.4

aEstimated total lagoon liquid includes total liquid manure plus average lagoon surface rainfall surplus; does not account for seepage. blrrigated: sprinkler irrigated liquid, uncovered for 1 month or longer. Soil incorporated: sprinkler irrigated liquid, plowed or disked into soil within 2 days.

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Table 2. Land Application Rate For Irrigated Swine Feeder-To-Finish Lagoon Liquid.

Rate-Cereal Tifton44 Bermuda

Limiting Corn Fescueb Tifton44b Grain Bermudac Hay

Nutrient

Maximum Pounds Per Acre Per Year

N 100 150 200 275 PzOs 50 60 75 75 Kp 80 100 100 225

Inches Per Acre Per Year

N 1.50 2.2 2.9 4.0 PzOs 1.30 1.6 2.0 1.0 K20 0.86 1.1 1.1 2.4

Minimum Acres Per Animal

N 0.023 0.015 0.012 0.0085 PPs 0.025 0.021 0.017 0.0170 K20 0.040 0.032 0.032 0.0140

•N leaching and denitrification and P205 soil immobilization unaccounted for. bopen grazing. ccontrolled grazing.

be monitored yearly to ensure a safe level. Electrical conductivity (EC) is a convenient field mea­surement that indicates salt con­tent. Before the salt content reaches 2,000 to 3,000 milligrams per liter (electrical conductivity of 3 to 5 millimhos per centime­ter), the lagoon should be pumped down and fresh water added. This will reduce the chance of bacterial inhibition and formation of magnesium ammonium phosphate or stru­vite. This struvite may form on the inside of pipes and pump impellers in the recycled flush system, eventually causing breakdown. For information on addressing this situation see Extension Circular ANR-860, "Controlling Salt Buildup In Wastewater Recycling Systems."

Pumping operations should be started before the lagoon is full to assure space (safety vol-

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ume) is always available to hold a 25-year-24-hour storm. Good management guidelines call for pumping the lagoon when the water level reaches 1 foot below the design water level (usually marked by a treated post on the inside slope of the last stage).

In a single-stage lagoon, per­manent markers should be in­stalled (1) at a mark 1 foot below design water level to show when to initiate pumping the lagoon and (2) at the lagoon treatment level to indicate when to stop pumping (see Figure 1). In a two-stage lagoon, a perma­nent marker is needed only in the second stage to indicate when to initiate pumping. Pumping out too much effluent is not a problem in the second stage if the 2-foot minimum depth remains to allow recycle pump operation (see Figure 2). The first stage is pumped only to remove accumulated solids which reduce the permanent treatment volume (lagoon reno­vation, once every 5 to 20 years, depending on design) .

325 400 85 100

260 300

4.8 5.9 2.3 2.7 2.8 3.2

0.0072 0.0058 0.0150 0.0130 0.0120 0.0110

Appearance And Safety Efforts should be made to

make a swine waste lagoon as aesthetically pleasing as possi­ble. Berms and embankments should have good grass cover for appearance and erosion con­trol and be mowed and main­tained on a regular basis. A well­maintained lagoon is less likely to attract attention and cause controversy.

The lagoon should be fenced to prevent access of children, trespassers, and livestock. Warning signs (SEWAGE TREAT­MENT FACILITY-KEEP OUT) should be posted and any access gate locked. ARCHIVE

References Agricultural Waste

Management Field Handbook. 1992. Part 651, National Engineering Handbook. Soil Conservation Service.

ASAE Engineering Practice: ASAE EP403.3. Design Of Anaerobic Lagoons For Animal Waste Management. ASAE Standards, 1996. St. Joseph, Missouri.

Barker, James C. 1995. Lagoon Design and Management For Livestock Waste Treatment And Storage. Circular EBAE 103-83. North Carolina Cooperative Extension Service. NC State University, Raleigh, North Carolina.

Barker, James C. 1990. Swine Production Facility Manure Management: Underfloor Flush Lagoon Treatment. Circular EBAE 129-80. North Carolina Cooperative Extension Service. NC State University, Raleigh, North Carolina.

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~ ALABAMA. .... COOPERATIVE~

ExtenSIOn SYSTEM

CIRCULAR ANR-973

Ted W. Tyson, Extension Agricultural Engineer, Associate Professor, Agricultural Engineering, Auburn University

Adapted from: Pfost, Donald, and Charles Fulhage. 1992. Lagoons For Storage/Treatment Of Dairy Waste . University Extension. University of Missouri-System, Columbia, MO.

Printed by the Alabama Cooperative Extension System in cooperation with the Alabama Depa1tment of Environmental Management and the Environmental Protection Agency with Clean Water Act Section 319 Demonstration Funds.

For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) of­fers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability. UPS, 2M23, New 8:96, ANR-973

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